Pain is one of the most common reasons for a patient to seek medical care and in consequence, pain results in a tremendous number of lost work days per year.
Pain is an unpleasant feeling often caused by intense or damaging stimuli, such as stubbing a toe, burning a finger, putting alcohol on a cut, and bumping the funny bone. The International Association for the Study of Pain's widely used definition states: “Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”. Pain motivates the individual to withdraw from damaging situations, to protect a damaged body part while it heals, and to avoid similar experiences in the future. Most pain resolves promptly once the painful stimulus is removed and the body has healed, but sometimes pain persists despite removal of the stimulus and apparent healing of the body; and sometimes pain arises in the absence of any detectable stimulus, damage or disease.
Pain is the most common reason for physician consultation. It is a major symptom in many medical conditions, and can significantly interfere with a person's quality of life and general functioning. Psychological factors such as social support, hypnotic suggestion, excitement, or distraction can significantly modulate pain's intensity or unpleasantness.
In 1994, responding to the need for a more useful system for describing chronic pain, the International Association for the Study of Pain (IASP) classified pain according to specific characteristics: (1) region of the body involved (e.g., abdomen, lower limbs), (2) system whose dysfunction may be causing the pain (e.g., nervous, gastrointestinal), (3) duration and pattern of occurrence, (4) intensity and time since onset, and (5) etiology.
This system has been criticized by Clifford J. Woolf and others as inadequate for guiding research and treatment. According to Woolf, there are three classes of pain: nociceptive pain (see hereunder), inflammatory pain which is associated with tissue damage and the infiltration of immune cells, and pathological pain which is a disease state caused by damage to the nervous system or by its abnormal function (dysfunctional pain, irritable bowel syndrome, tension type headache, etc.).
In nociceptive pain, the stimulation of the sensory nerve endings called nociceptors causes the sensation of pain. Such pain often occurs after injury or surgery. The pain signals are transmitted by the nociceptors to the brain. Often the pain is localised, constant and has an aching or throbbing quality. Once the damage to the tissue heals the pain usually resolves. Treatment with opioids may resolve nociceptive pain. Psychogenic pain is a pain disorder that is associated with psychological factors. Some types of mental or emotional problems can cause pain. They can also increase or prolong pain. Stomach pain is one of the most common types of psychogenic pain. People with this pain disorder actually have real pain. The diagnosis is made when all physical causes of pain are ruled out.
Neuropathic pain is caused by abnormalities in the nerves, spinal cord or brain and is a chronic type of non-malignant pain with an estimated prevalence of over 1% of the population. Optimizing pain relief in these patients is crucial in helping a patient regain control of his or her life. The most common cause of neuropathic pain is injury or dysfunction of nerves. Injury or dysfunction of peripheral nerves or nerves descending from the spinal cord results disinhibition of nerve impulses at the spinal cord which in consequence results in pain. Neuropathic pain can also be centrally mediated, rather than peripheral, in conditions such as spinal cord injury and multiple sclerosis.
Neuropathic pain can therefore be divided into two further classes; peripheral neuropathic pain and central neuropathic pain depending on whether the peripheral or central nervous system is affected.
Inadequate treatment of pain is widespread throughout surgical wards, intensive care units, accident and emergency departments, in general practice, in the management of all forms of chronic pain and in end of life care. This neglect is extended to all ages, from neonates to the frail elderly. African and Hispanic Americans are more likely than others to suffer needlessly in the hands of a physician; and women's pain is more likely to be undertreated than men's.
Therefore, it is needed to develop therapeutic measures for treating or alleviating pain.